Electro-mechanical transducer



y 1966 J. HAYER, JR, ETAL 3,252,016

ELECTRO-MECHANICAL TRANSDUCER Filed Sept. 11, 1962 IN VENTORS 'tioned patents.

3,252,616 ELECTRQ-MECHANICAL TRANSDIKIER John Hayer, .lr., Highland Park, and Eric J. Straus, Westfield, NJL, assignors to Gulton Industries, Inc., Metuchen, Ni, a corporation of New Jersey Filed Sept. 11, 1962, Ser. No. 222,835 .13 Claims. (Cl. SIG-8.4)

The principal object of this invention is to provide an improved electro-mechanical transducer, which is adaptable for converting mechanical energy into an electrical signal, which is particularly adaptable for use as an accelerometer for producing electrical signals in accord- I United States Patent ance with vibrations applied thereto, which may be adaptable for converting electrical energy to mechanical energy, and which has arelatively high resonant frequency and also a relatively high sensitivity.

Briefly, the electrormechanical transducer of this invention includes a base, and a substantially circular disc shaped armature which is secured at the peripheral edge thereof and at an annular area of one face thereof adjacent the peripheral edge thereof to the base with the other face thereof free from the base. At least one thin piezoelectric element provided with electrodes is secured in face abutting relation to the armature, and means are provided for applying flexing forces to the armature for flexing the same.

Since, in accordance with this invention, the armature is secured at its periphery to the base, a substantially rigid structure is provided which has a relatively high reso-. nant frequency, especially as compared to the resonant frequency of a substantially circular armature which is secured at its center, as in the electro-mechanical transducers disclosed in Dranetz Patent No. 2,808,522 and Dranetz et al. Patent No. 2,967,956, which are not so nearly rigid a structure. If in peripherally securing the armature to the base to provide high resonant frequency, the armature were annularly secured to the base at the periphery and at both faces thereof, as by clamping the armature to the base by an annular ring or the like, the

structure would be extremely rigid and high resonant frequency, free to flex. As a result, tro-mechanical transducer have an extremely and the armature would not be the sensitivity of such an elecwould be extremely low.

However, as expressed above, in accordance with this invention, the armature is secured to the base only at the peripheral edge thereof and at an annular area on only one face thereof adjacent the peripheral edge thereof with the other face thereof free from the base. As a result, a substantially rigid structure is provided to provide high resonant frequency but, yet, the free face of the armature permits deformation contours to exist therein and allow relatively free flexing of the armature for providing relatively high sensitivity of the electro-mechanical transducer of this invention. Thus, greatly increased sensitivity with very little decrease in resonant frequency is provided by this-invention over the aforementioned extremely rigid construction, and, also, the electro-mechani cal transducer of this invention has considerably higher resonant frequencies and greater sensitivities than the center mounted armature transducers of the aforemen For example, in connection with the latter, actual tests show that for same diameter armatures and same sized piezoelectric elements, the transducer with the armature peripherally secured in accordance with this invention had a sensitivity (mv./g.) of -13 and a resonant frequency of 50 kc., While the transducer with the armature centrally secured had a sensitivity (mv./g.) of 8.5 to 12 and a resonant frequency of 25 kc.

The peripheral securing of the armature to the base for achieving the results of this invention may be accomplished in various ways. For example, the base may have thereof adjacent the 3,252,016 Patented May 17, 1966 a substantially circular cavity and a substantially circular annular shoulder in the cavity, and the substantially circular disc shaped armature may be secured, as by force fit or the like, in the cavity with the peripheral edge thereof engaging the cavity, with an annular area of one face peripheral edge thereof engaging the annular shoulder and with the other face thereof free from the base. As another example, there may be provided a substantially circular disc shaped armature integrally formed on one end of the base so that the armature is effectively secured at its peripheral edge and at an annular area of one of its faces adjacent its peripheral edge to the base with its other face free from the base.

The armature may be flexed in various ways, as by applying electrical energy to the electrodes of the piezoelectric element to produce mechanical movement of the armature, or by applying mechanical energy to the armature to produce electrical signals at the electrodes of the piezoelectric element. However, the electromechanical transducer of this invention is particularly suited fo use as an accelerometer and, here, means are provided for securing the base to an object to be vibrated for vibrating the base and flexing the armature to stress the piezoelectrio element for producing electrical signals at the electrodes of the piezoelectric element in accordance with such vibrations. In order to increase still further the sensitivity of the accelerometer, a mass may be suitably secured to the center of the armature for mass loading the armature but this will operate to decrease somewhat the resonant frequency of the accelerometer.

Further objects of this invention reside in the details of construction of the electromechanical transducer and in the cooperative relationships between the component parts thereof.

Other objects and advantages of this invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawing, in which:

FIG. 1 is a partial vertical sectional view through one form of the electro-mechanical transducer of this invention;

FIG. 2 is a partial vertical sectional view through an other form of this invention;

FIG. 3 is a partial vertical sectional view through a further form of this invention;

FIG. 4 is a partial vertical sectional view through still another form of this invention;

FIG. 5 is a partial vertical sectional view through still a further form of this invention; and

FIG. 6 is a top plan transducer illustrated in FIG. 1.

One form of the electro-mechanical transducer of this invention is generally designated at 10 in FIGS. 1 and 6. 'It includes a base 11 which may be formed of any suitable material, such as steel or the like, and which may be generally circular in configuration. The base 11 is integrally provided with a screw threaded extension 12 and a flange 13 for securing the base 11 to an object to be vibrated so as to vibrate the base 11 in accordance with the vibrations of the object. The base 11 is provided with a substantially circular cavity 14 and a substantially circular annular shoulder 15 in the cavity.

The transducer or accelerator 10 also includes an arm-ature 16 which is made of suitable material, such as steel or the like, and which is preferably substantially circular in configuration. A thin piezoelectric element, preferably formed of a suitable piezoelectric ceramic, such as barium titanate, lead-zirconium-titanate or the like, is provided with suitable electrodes on the faces thereof and is secured in face abutting relation to the armature 16. The ceramic element 17 is permanently view of the electro-mechanical 3 polarized so as to make it piezoelectric, that is, to produce electrical signals at its electrodes in accordance with the flexing of the armature 16. The armature 16 may also carry in face abutting relation another ceramic element, which may be of the materials described in connection with the ceramic element 17 and which is also provided with electrodes on the opposite faces thereof. This ceramic element 18 may also be permanently polarized for producing electrical signals in accordance with the flexing of the armature 16. The piezoelectric ceramic elements 17 and 18 may be electrically connected into a circuit by suitable leads attached to the electrodes thereof for series or parallel output depending upon the desired effects required such as increased capacitance, increased sensitivity, sensitivity cancellation and the like. Also, one or-the other of the ceramic elements 17 and 18 may be unpolarized so as to providetemperature compensation or the like. The electroded ceramic elements 17 and/ or 18 may be secured to the armature 16 in any suitable manner as by soldering, cementing or the like.

The substantially circular disc shaped armature 16 with the ceramic element 17 and 18'secured thereto is secured in the cavity 14 of the base 11 with the peripheral edge of the armature 16 engaging the cavity, with an annular are-a of one face of the armature adjacent the peripheral edge thereof engaging the annular shoulder 15, and with the other face of the armature being free from the base. This peripheral securing of the armature 16 in the base 11 may be accomplished in any suitable manner as by force fit or the like. Since the armature is secured to the base only at the peripheral edge thereof and at an annular area on only one face thereof with the other face thereof free from the base, a substantially rigid structure is provided to provide high resonant frequency but, yet the free face of the armature permits deformation contours to exist therein and allow relatively free flexing of the armature. for providing relatively high sensitivity for the electro-mechanical transducer. As the base 11 is vibrated, the armature 16 is flexed to stress the ceramic elements 17 and/or 18 to produce electrical signals at the electrodes thereof in accordance with the vibrations imparted to the base 11, there being provided relatively high resonant frequency and also relatively high sensitivity.

Another further form of the transducer of this invention is generally designated at 20 in FIG. 2, it being substantially the same as the aforementioned transducer and accordingly, like reference characters have been utilized for like parts. In the transducer 20, the ceramic element 18 is permanently polarized so as to produce eletrical signals at the electrodes thereof in accordance with vibrations imparted to the base 11. In the transducer 20 of FIG. 2, a mass 21 of suitable material such as steel, or the like, is centrally secured to the armature 16 so as to mass load the armature 16. The mass 21, which is secured as closely as possible to the center of the armature 16, in mass loading the armature, operates to increase the sensitivity of the accelerometer but, in so doing, the resonant frequency of the accelerometer is decreased somewhat. Thus, the accelerometer 20 may be utilized in lieu of the accelerometer 10 where increasd sensitivity and decreased resonant frequency are desired. Outside of this, the accelerometer 20 of FIG. 2 operates in the same manner as the accelerometer 10 of FIG. 1;

A further form of the accelerometer of this invention tion to provide relatively high resonant frequency and cured in an annular recess 30, as by force fit or the like,

' of a base member 29 which, in turn, is provided with a screw threaded extention 31 and a flange 32 for mounting the same on an object to be vibrated.

A piezoelectric ceramic element 33 of the type described above and provided with electrodes on its opposite faces is suitably secured to the armature 26 in face abutting arrangement. The base 27 may be provided with an annular extension 34 to assist in centering the ceramic element 33 on the armature 26. As the base 27 is vibrated through the base member 29 by the object being vibrated, the armature 26 is flexed to stress the piezoelectric element 33 for producing electrical signals at the electrodes thereof in accordance with such vibrations. Accordingly, the transducer 25 of FIG. 3 operates iu the same manner as the transducer 10 of FIG. 1, it having relatively high resonant frequency and relatively high sensitivity.

A modified form-of the transducer of this invention is generally designated at 40 in FIG. 4, it having the same armature base and piezoelectric element as the transducer 25 of FIG. 3. Accordingly, like reference characters have been utilized for like parts. In FIG. 4, however, the base member 42 is provided with a central circular boss 41 to which is secured, as by force fit or the like, the base 27. The base member 42 isprovided with a screw threaded extension 43 and flange 44 for mounting the same on an object to be vibrated. The essential differences between the transducer 40 of FIG. 4 and the transducer 25 of FIG. 3 is in the manner of securing the base to the base member." Outside of this difference, the transducers and 25 are the same and operate in the same manner to produce the same results.

The transducer generally designated at in FIG. 5 corresponds to the transducer 25 of FIG. 3, and like reference characters have been utilized for like parts. Here,

is generally designated at 25 in FIG. 3. It includes a substantially circular armature 26 which is integrally formed with a hollow, substantially circular base 27, the armature 26 being effectively secured at its peripheral edge and at an annular area of one of its faces to the base with its other face free from the base as indicated by dotted lines 28 in FIG. 3. Thus, the integrally formed armature and base of FIG. 3 corresponds to the separable a-rmature and base of FIG. 1 in manner of operaa piezoelectric ceramic element 51, formed of materials such as described above and provided with electrodes on the opposite faces thereof, is suitably secured in face abutting relation to the armature 26 so as to be stressed in accordance with the flexing of the armature 26. Here also, a mass 52 is centrally secured to the armature 26 for increasing the sensitivity of the accelerometer which, in turn, decreases somewhat the resonant frequency thereof. Basically the transducer 50 of FIG. 5 differs from the transducer 25 of FIG. 3 in substantially the same Way as the transducer 20 of FIG. 2 differs from the transducer 10 of FIG. 1, and accordingly, a further description of the operation of the transducer 50-of FIG. 5 is not considered necessary.

While for purposes of illustration several forms of this invention have been disclosed, other forms thereof may become apparent to those skilled in the art upon-reference to this disclosure and, therefore, this invention is to be limited only by the scope of the appended claims.

We claim as our invention: I

1. An electro-mechanical transducer comprising a base, a substantially circular disc shaped armature secured at the peripheral edge thereof and at an annular area of one face thereof adjacent the peripheral edge thereof to the base with the other face thereof free from. the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature so as to flex with the armature, and means for applying flexing forces to the armature for flexing the same.

2. An accelerometer comprising a base, a substantially circular disc shaped armature secured at the peripheral edge thereof and at an annular area of one face thereof adjacent the peripheral edge thereof to the base with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature to be stressed in a flexural mode as the armature is flexed, and means for securing the base to an object to be vibrated for vibrating the base and flexing the armature to stress the piezoelectric element for producing electrical signals at said electrodes in accordance with said vibrations.

3. An electro-mechanical transducer comprising a base having a substantially circular cavity and a substantially circular annular shoulder in the cavity, a substantially circular disc shaped armature secured in the cavity with the peripheral edge thereof engaging the cavity, with an annular area of one face thereof adjacent the peripheral edge thereof engaging the annular shoulder and with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature so as to flex with the armature, and means for applying flexing forces to the stantially cylindrical hollow base and a substantially circular disc shaped armature integrally formed on one end of the base so that the armature is effectively secured at its peripheral edge and at an annular area of one of its faces adjacent its peripheral edge to the base with its other face free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature so as to flex with the armature, and means for applying flexing forces to the armature for flexing the same.

' 5. An electro-mechanical transducer comprising a base, a substantially circular disc shaped armature secured at the peripheral edge thereof and at an annular area of one face thereof adjacent the peripheral edge thereof to the base with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature so as to flex with the armature, and means for applying flexing forces to' the armature for flexing the same.

6. An electro-mechanical transducer comprising a base having a substantially circular cavity and a substantially circular annular shoulder in the cavity, a substantially circular disc shaped armature secured in the cavity with the peripheral edge thereof engaging the cavity, with an annular area of one face thereof adjacent the peripheral edge thereof engaging the annular shoulder and with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature so as to flex wtih the armature, and means for applying flexing forces to the armature for flexing the same.

7. An electro-mechanical transducer comprising a substantially cylindrical hollow base and a substantially circular disc shaped armature integrally formed on one end of the base so that the armature is effectively secured at its peripheral edge and at an annular area of one of its faces adjacent its peripheral edge to the base with its other face free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature so as to flex with the armature, and means for applying flexing forces to the armature for flexing the same.

8. An electro-rnechanical transducer for converting mechanical energy into an electrical signal comprising a base, a substantially circular disc shaped armature secured at the peripheral edge thereof and at an annular area of one face thereof adjacent the peripheral edge thereof to the base with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature to be stressed in a flexural mode as the armature is flexed, and means for applying mechanical flexing forces to the armature for stressing the piezoelectric element to produce corresponding electrical signals at said electrodes.

9. An accelerometer comprising a base, a substantially circular disc shaped armature secured at the peripheral edge thereof and at an annular area of one. face thereof adjacent the peripheral edge thereof to the base with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature to be stressed in a flexural mode as the armature is flexed, and means for securing the base to an object to be vibrated for vibrating the base and flexing the armature to stress the piezoelectric element for producing electrical signals at said electrodes in accordance with said vibrations.

10. An accelerometer comprising a base having a sub-v to the armature to be stressed in a flexural mode as the armature is flexed, and means for securing the base to an object to be vibrated for vibrating the base and flexing the armature to stress the piezoelectric element for producing electrical signals as said electrodes in accordance with said vibrations. I

' 11. An accelerometer comprising a substantially cylindrical hollow base and a substantially circular disc shaped armature integrally formed on one end of the base so that the armature is effectively secured at its peripheral edge and at an annular area of one of its faces adjacent its peripheral edge do the base with its other face free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature to be stressed in a flexural mode as the armature is flexed, and means for securing the base to an object to be vibrated for vibrating the base and flexing the armature to stress the piezoelectric element for producing electrical signals at said electrodes in accordance with said vibration.

12. An accelerometer comprising a base having a substantially circular cavity and a substantially circular annular shoulder in the cavity, a substantially circular disc shaped armature secured in the cavity with the peripheral edge thereof engaging the cavity, with an annular area of one face thereof adjacent the peripheral edge thereof engaging the annular shoulder and with the other face thereof free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature to be stressed in a flexu-ral mode as the armature is flexed, and means for securing the base to an object to be vibrated for vibrating the base and flexing the armature to stress the piezoelectric element for producing electrical signals at said electrodes in accordance with said vibrations.

13. An accelerometer comprising a substantially cylindrical hollow base and a substantially circular disc shaped armature integrally formed on one end of the base so that the armature is effectively secured at its peripheral edge and at an annular area of one of its faces adjacent its peripheral edge to the base with its other face free from the base, said armature so secured having a relatively high resonant frequency and being relatively free to flex, a mass secured to the center of the armature for mass loading the armature, at least one thin piezoelectric element provided with electrodes and secured in face abutting relation to the armature to be stressed in a flex- References Cited by the Examiner UNITED STATES PATENTS 1/1961 Massa 310-85 OTHER REFERENCES Bell Telephone System Technical Publications, Acceleration Eflects on Electron Tubes, page 8, September 1953. Originally published in The Bell System Technical Journal; volume 33, September 1953.

ORIS L. RADER, Primary Examiner.

MILTON O, HIRSHFIELD, Examiner. 

1. AN ELECTRO-MECHANICAL TRANSDUCER COMPRISING A BASE, A SUBSTANTIALLY CIRCULAR DISC SHAPED ARMATURE SECURED AT THE PERIPHERAL EDGE THEREOF AND AT AN ANNULAR AREA OF ONE FACE THEREOF ADJACENT THE PERIPHERAL EDGE THEREOF TO THE BASE WITH THE OTHER FACE THEREOF FREE FROM THE BASE, SAID ARMATURE SO SECURED HAVING A RELATIVELY HIGH RESONANT FREQUENCY AND BEING RELATIVELY FREE TO FLEX, AT LEAST ONE THIN PIEZOELECTRIC ELEMENT PROVIDED WITH ELECTRODES AND SECURED IN FACE ABUTTING RELATION TO THE ARMATURE SO AS TO FLEX WITH THE ARMATURE, AND MEANS FOR APPLYING FLEXING FORCES TO THE ARMATURE FOR FLEXING THE SAME. 